Reconstitution Drug Calculation Problems

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Hello! I am studying for an upcoming drug calculation test and have been having a lot of trouble with reconstitution problems.

For example:

Order Ancef 225 mg IM q 6 hr. The vial reads Ancef 250 mg. Add 2 ml of diluent to provide 130 mg/ml.

or

Solumederol 100 mg IM now. The vial reads Solumederol 100 mg. Add 2ml of diluent to yield 100 mg/1.2ml.

I just feel like I don't even know where to begin and it's a little frustrating.

Any help would be appreciated! Thank you!

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The way those are worded makes it pretty simple. Ignore how much you add to dilute, and just worry about the final mg/mL concentrations that follow "to yield" or "to provide".

It gets trickier when there are problems where the label gives you different choices of concentration.

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Specializes in Med/Surg, Academics.
jessicalane said:
Hello! I am studying for an upcoming drug calculation test and have been having a lot of trouble with reconstitution problems.

For example:

Order Ancef 225 mg IM q 6 hr. The vial reads Ancef 250 mg. Add 2 ml of diluent to provide 130 mg/ml.

or

Solumederol 100 mg IM now. The vial reads Solumederol 100 mg. Add 2ml of diluent to yield 100 mg/1.2ml.

I just feel like I don't even know where to begin and its a little frustrating.

Any help would be appreciated! Thank you!

As the poster above explained, you ignore the amount of diluent...it's throwing you off. The instructions from pharmacy give you the concentration. Ancef is 130 mg/ml after reconstitution. Solumederol is 100 mg/1.2 ml after reconstitution.

Just do the cross multiply and divide method on the Ancef, and you have the mls to administer. For the Solumederol problem, the answer is in the question itself.

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I feel so silly now! That was so simple, just like a regular Dr. Order problem! The diluent part is what was throwing me off, and it wasn't even necessary to solve the problem! Thanks for your help you guys!

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Specializes in Med/Surg, Academics.
I feel so silly now! That was so simple, just like a regular Dr. Order problem! The diluent part is what was throwing me off, and it wasn't even necessary to solve the problem! Thanks for your help you guys!

Don't feel silly at all. Sometimes it's difficult to deal with distractors in a problem, and I think the 2 ml was definitely distracting! Good luck!

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I have a problem similar to. I don't know how to tackle it. If anyone could help I would appreciate it. I'm sure if I saw how to work out the problem I'm sure to understand it. My teacher isn't the greatest at explaining things. Thank you.

Your patient is to receive Gentamycin 150 mg IVPB q18h. You have to constitute the powdered form of the medication. The Gentamycin comes in a 260 mg multidose vial. The directions state that after reconstituting with 3.6 ml of sterile water there will be a volume of 4 ml in the vial. After reconstitution the medication must be mixed in 100 ml D5W and infused over 45 minutes. The drip factor of the IV is 20 gtt/ml.

1. After reconstitution, what is the strength of the gentamycin in the vial?

2. What volume of medication will you remove from the vial in order to administer the required dosage?

&

3. What will the drip rate (gtt/min) be for the IVPB?

PLEASE HELP!!!!

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Specializes in Pediatrics.

Your patient is to receive gentamycin 150 mg ivpb q18h. You have to constitute the powdered form of the medication. The gentamycin comes in a 260 mg multidose vial. The directions state that after reconstituting with 3.6 ml of sterile water there will be a volume of 4 ml in the vial. After reconstitution the medication must be mixed in 100 ml d5w and infused over 45 minutes. The drip factor of the iv is 20 gtt/ml.

1. After reconstitution, what is the strength of the gentamycin in the vial?

Strength (I'm assuming) is referring to the "concentration" or "yield" in the vial. You get this by knowing how much volume and how many mg are in the vial.

2. What volume of medication will you remove from the vial in order to administer the required dosage?

So, after you get your "strength" you need to set up your equation to figure out how much you'll need for your dose (which is 150mg. Either ratio/proportion, desired / have x ml, or dimensional analysis.

3. What will the drip rate (gtt/min) be for the ivpb?

You need to set up your equation with the 3 numbers you need: volume (in the bag), drop factor, and time (that it will run over).

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Thank you

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Hello. I am working on a practice test which provides the answers in the back. No matter what I do, my answers do not match, so clearly I am doing something VERY wrong. I have looked high and low and can not find a formula that I seem to be able to make work to get their answer !

Order: Ampicillin 500 mg

Available: Ampicillin 500 mg

Directions: Reconstitute with 1.8 mL sterile water for a concentration of 250 mg/ml

Their answer is 2ml.

Order ancef 500 mg

Available : ancef 1 G

Directions reconstitute with 2.5 mL normal saline to yield 3 mL worth a concentration of

330 mg/mL

Their answer is 1.5 mL

Any and all help is greatly appreciated

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Specializes in PICU, Sedation/Radiology, PACU.

As the first posts in this thread say, you need to ignore how much is available and the volume you use to reconstitute. The only things you need to know are the ordered dose, and the concentration of the medication.

Order: Ampicillin 500 mg

Available: Ampicillin 500 mg

Directions: Reconstitute with 1.8 mL sterile water for a concentration of 250 mg/ml

Their answer is 2ml.

All you need is the information in bold. Forget everything else. So then your question reads: Ampicillin is supplied as 250mg/mL. How many mL's do you give if the ordered dose is 500mg?

Then you just follow your standard medication formula: Desired dose / Available concentration x available volume.

500mg (desire dose) / 250mg (available concentration) x 1mL (available volume) = 2mL of medication

For your second problem the only information you need is:

Order ancef 500 mg

Concentration of 330 mg/mL

500mg (desired dose) / 330 mg (available concentration) x 1mL (available volume) = 1.5 mL

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